In recent years, the electronic equipment and telecommunications industries have experienced significant growth. One reason for the success of such industries relates to their ability to develop appliances such as computers, tape players, televisions, telephones and other devices that are increasingly smaller, thinner and more portable. The ability to miniaturize electronic and telecommunication components has been made possible at least partially through developments in the field of electronics packaging.
Electronic packages are used to mount integrated circuit (IC) chips to substrates such as printed circuit boards. Electronic packages physically and electrically connect the integrated circuit chips to the substrates and protect the chips from hostile environments. The package provides a means by which electrical connection can be made from the finely spaced electrodes or electrical contact pads of the IC chip to the more coarsely spaced circuitry of the printed circuit board. Common types of techniques for connecting IC chips to electronic packages include tape automated bonding, wire bonding, and flip chip solder bumping. Of the three techniques, solder bumping is experiencing increased popularity because it provides precise, reliable connections at high packaging densities.
Electronic packages have been traditionally connected to printed circuit boards by means of sets of connecting conductors arranged around the periphery of the package which, depending on their shapes, are called "J" leads or "gull-wing" leads. These leads are soldered to corresponding pads on the printed circuit board using surface mount technology. As the spacing or pitch of these peripheral leads has decreased, connection of these leads has become more difficult. To address this problem, arrays of solder balls are increasingly replacing peripheral leads as a means to make electronic connection between packages and printed circuit boards. These arrays, commonly called ball grid arrays or BGA's, can be spread over the full area of the bottom of the electronic package rather than just the peripheries, thus lessening the need for fine pitch.
Ball grid arrays commonly use a plurality of solder balls arranged in an array to provide a connection between an electronic package and a substrate such as a printed circuit board. Typically, the solder balls of the array are positioned between conductive pads or terminals on the electronic package and conductive pads or terminals on the substrate. Once the package has been properly aligned with the substrate, the solder balls are melted and then cooled such that connections are made between the pads of the package and the pads of the substrate.
Solder balls can be manufactured by a variety of techniques. Exemplary techniques include direct casting (U.S. Pat. Nos. 5,388,327 and 5,381,848), dipping solder wettable pads in molten solder (U.S. Pat. No. 4,950,623), melting portions of cut off wires (U.S. Pat. Nos. 4,661,192 and 3,380,155) reflowing solder paste within recesses or wells (U.S. Pat. Nos. 5,024,372 and 5,133,495), evaporation of solder through masks (U.S. Pat. No. 3,458,925), and cutting a thin film of metal into chips and melting the chips against a ceramic jig having recesses which collect microspheres of the melted metal (Japanese Patent Application 4-262895).
A variety of techniques can be used to arrange solder balls in arrays. Exemplary techniques include using adhesive to hold pre-formed solder balls in a desired array on a flat carrier tape (U.S. Pat. Nos. 5,323,947 and 3,719,981), partitioning a metal film and then melting the film to form an array of microbeads (U.S. Pat. Nos. 5,366,140 and 5,486,427), positioning loose balls using a vacuum placement tool (U.S. Pat. No. 5,284,287), and positioning balls using a template (U.S. Pat. No. 5,504,277).
The competitive nature of the electronics industry combined with the need for smaller and thinner electronic components generates special concerns for electronic package designers. For example, one concern relates to reducing the cost of electrical connecting techniques such as solder bumping and ball grid arrays. A concern specific to solder bumping and ball grid arrays includes providing solder balls having uniform sizes. Another concern specific to solder bumping and ball grid arrays includes providing solder ball arrays having solder balls precisely aligned at desired locations. The present invention addresses these concerns as well as other concerns.